The human ear is very sensitive to damage by high levels of noise, including damage caused by high amplitude bursts of noise, and by long term exposure to high levels of noise. Various devices for protecting the ear from excessive levels of sound have therefore been developed. However, in addition to requiring ear protection in a noisy environment, a user often must be able to hear and understand certain sounds, such as conversation, warning sirens or other communication, while in the noisy environment. Such a situation can arise in a factory or other environment with high and potentially damaging levels of background noise.
To address this situation, various devices have utilized signal processing techniques in attempts to suppress unwanted noise while still allowing the user to hear desired sounds. These techniques have included low pass filtering or a combination of low and high pass filtering, as well as attenuation of large amplitude audio signals. However, these techniques often attenuate or filter out frequencies important to the communication desired to be heard. In addition, devices that clip or reject some frequencies of the human voice can distort sound quality, and the result can be acoustically unpleasant and interfere with understanding.